Widely known in the present state of the art are rotors comprising disks installed opposite each other and carrying concentrically disposed impact elements (cf., U.S. Pat. No. 3,047,243, Int.Cl. B 02c published in 1962).
In prior-art rotors the working surface of the beater elements wears substantially unevenly. This is explained by the fact that the velocity of the material as it strikes the beater element is much higher than the velocity of the material moving along the working surface of the beater element caused by centrifugal forces. Because of this, the portion of material being processed by the beater working surface fails to be removed completely from its surface by the time a fresh portion of material comes in to be processed. As a result, part of the material tends to stick to the working surface at locations more distant from the center of rotation of the rotor whereas the working surface area adjacent to the center of rotation of the rotor tends to be exposed. Every fresh portion of the inflowing material lands on the exposed beater working surface at locations near by the center of rotation of the rotor, and on a layer of material protecting the beater surface from wear, at the beater periphery.
Besides, particles of the material being hurled on the beater working surface are affected by aerodynamic drag with the result that the velocity of their impingement upon the beater surface is less, due to a longer path of travel, at the beater periphery than at locations near the center of rotation of the rotor.
For the reasons given above, the beater working surface will wear unevenly and the portion adjacent to the center of rotation of the rotor will wear faster than that at the beater periphery. This brings about a change in the profile of the working surface and, hence, in the angle of impingement of particles of the material upon the beater working surface which leads to changes in the grain size composition of the finished product.
Attempts have been made to extend the beater service life by hardening its working surface at the extreme points and at the center thereof (cf., accepted Application No. 2,319,810, Federal Republic of Germany, Int. Cl..sup.2 B 02c 13/22).
However, such a hardening fails to prevent distortions of the working surface profile resulting from variable intensity of the abrasive action produced by feed on the hard-faced portions made of the same material.
Besides, the hard-faced member secured closest to the center of rotation of the rotor is so disposed that the less wear-resistance material, wherein it is held is subjected to rapid wear with attendant fallout of the said member.